Possible camshaft wear, tappets, CU engine, advice please

[Paul Weeding]

I'd back them all off half a turn and see if she starts

[kevtherev]

Ok
There is 4mm of travel in a lifter you preloaded 1.5 mm
It could be that they are solids after all.

[937carrera]

Good idea Paul, I think I'll adjust each cylinder one at a time and use my leak tester to see how far I need to wind out the adjusters to get a seal again.

Looking back over the history file Kev I did notice a set of 8 hydraulic tappets were fitted, with another pair fitted a relatively short period later. The comment on the invoice from last month about the tappets being "stripped out and modified to get engine running again" is starting to make sense, though I'm not sure if the modification was to the cam followers (what / how) or simply the valve lash.

[937carrera]

I have had an opportunity to spend a bit of time on the T25 this evening.

I decided to simply back the adjuster off half a turn at the time and see what happened, here's how it went:

1 1/2 turns (the starting point) - no compression
1 turn - no compression
1/2 turn - signs of some compression
No turns / nil lash - compression but not running
-1/2 turn - started and ran, but only revved to ~3600 rpm

After putting a bit of heat into the engine I then went round and set the tappets to 0.2mm, which is effectively where the van was when i bought it. This started better, was quicker to pick up and revved to 4100 rpm again. I guess this is about -1/4 turn

I could have another go at the weekend using the leak tester to try and optimise things a bit more, but I'm still struggling to work out what is wrong. It appears as though the valve stems are effectively too long to adjust the tappets correctly. I can't see that the valves would really be too long (unless all valve seats been machined excessively when the top end rebuild was done) so am wondering that the heads may have been machined / barrells shaved to increase compression but effectively lengthen the push rods Any other ideas ?

[kevtherev]

Put the adjustment to zero lash
Then do the same compression test.

[937carrera]

A quick update from todays activities.

I warmed the engine up and then removed the aircleaner etc and noticed that the choke was not in the correct position and it seemed to be stuck. I dismantled the carb, made sure the choke operated through the full range of movement (even though the part that touches the bimetallic strip was broken) and restarted the engine.

With the covers off I could see that theer was some minor backfiring in the same right hand carb above 3000 rpm.

I then tried out my new cheapo dial gauge on the tappets and saw around 4.2mm of movement on the inlet, about 3.4mm on exhaust.Is that anything like expected?

Then I adjusted the tappets to zero lash (around 1/3 of a turn) and restarted the engine again.It started, but was more difficult to start needing a little bit of throttle,it ticked overalright but was clearly running rougher, was rocking due to cylinder imbalance and when revved above 3000 rpm would have little backfires in both carbs.

I didn't have chance to do a compression test today, any further thoughts at this point ?

[937carrera]

Here's a couple of pictures from the right hand side carb - what I forgot to mention above was that the choke plate was bent & distorted, not only sticking



and this was the view down before I stripped the choke out - the pipe for the fuel flow from the accelerator pump was also bent and seemed out of place

[937carrera]

This morning I have had the compression and leak testers out, I started with a warm engine but it was cold by the time I finished. I did a normal leak test then increased the pressure to better identify any leaks,results as follows:

No1
115psi
30 % leakage with air bypassing into the crankcase breather. When I blocked that off the sound seemed as though it was coming up number 1 pushrod tubes

No2
120psi
55% leakage with a leak from the exhaust. I wound the tappet out to zero lash which stopped the exhaust leak and leakage was down to 40% with air bypassing through No1 pushrod tubes

No3
125psi
55% leakage with a leak from the exhaust. I fixed this again by adjusting to zero lash but leakage remained about 55% with air bypassing through No1 pushrod tubes

No4
130psi
34% leakage with air bypassing through No1 push rod tubes

I am about to re-assemble but it's curious how crankcase pressue is relieving it itself by preference through No1 pushrod tubes. You can't actually feel the airflow, but putting a rag over the holes changes the sound.

[937carrera]

Signs of progress

It wasn't running brilliantly when I restarted the engine, and the benefit of having the covers off the carbs was I could see little backfires in the right hand carb.

After getting the engine warm I decided to redo numbers 1 and 2, and essentially set to zero lash plus a tiny bit of play. I then reperformed the leak test, but this time not focussing on the value obtained, but on any leaks at higher pressure.

When doing number 1 again I just saw tiny wisps of vapourised fuel coming up the intake. I squirted some carb cleaner down and saw very clear wisps of vapur coming out of the intake. Having checked that there was a tiny amount of play in the tappets, which there was, then the conclusion seems to be that number 1 intake valve is not seating properly.

If that's the case then perhaps that's allowing some ignition of the air/fuel mix in the carb when number 1 fires Number 1 probably isn't running so well and perhaps number 2 isn't getting sufficient mixture to run properly as a consequence. That's my theory anyway .......

[Paul Weeding]

Are you in a position where you can pull the engine and pop the heads off??

The CU in the T25 has a pretty hard life... I've stripped a few, and they're more likely to burn out exhaust valves and seats than their T2 counterparts!!

[937carrera]

Thanks Paul,

I could drop the engine out and have a look at the heads....... but I don't want to at the moment.

The camper has (the usual) bodywork issues, which I need to sort out before it will get an MOT. My experience on mechanicals is much greater than on bodywork and I don't want to make the T25 immobile by taking the engine out because it's easier for me than addressing the bodywork side. At the moment it's fine for moving around the workshop, if I take the engine out I'll be stuck.

Given that the history file shows it had a top end rebuild less than 10,000 miles ago I was hoping that the top end would be fine and that there might be some alternative to an engine out and (full) strip down. It might just be the top end that needs doing, but having seen the comression test results and the ring bypass from the leak tests I think I'll be doing a full rebuild. That will probably have to wait until the bodywork side is sorted and maybe do the mechanicals while it is being painted ?

Do the CU engines in the T25 work that much harder than in a T2. I know they are bigger / heavier, but thought that the drag coefficient was better, or is it just that they tend to run a bit too hot if not looked after properly. Maybe I'll just have to make it into a 2.4